1. Field of the Invention
The present invention relates to a cryopump system and a method of operating the same, and a compressor unit suitable for use in the cryopump system.
2. Description of the Related Art
It is known to change the capacity of a helium compressor by controlling the rotational speed of a variable speed motor of the helium compressor. The compressor supplies a high pressure helium gas to an expansion type refrigerator.
A control range of the rotational speed of the motor is limited by specifications of the motor. Therefore, the capacity of the compressor can be merely changed within the limited range.